p53 is a tumor suppressor gene product identified in a wide variety of tumors. p53 protein accumulates within the malignant cells where it can be readily detected by immunohistochemistry. p53 protein is present in low concentrations in normal cells, but elevated levels of mutant p53 have been found in many common cancers. Accumulation of mutant p53 detected by immunohistochemical staining has been reported in breast, lung, colon, stomach, bladder, and testis carcinomas, soft-tissue sarcomas, and melanomas.